Paragon Corporation wrote:
Nick,
Okay we are seeing the same issue with our fastfoods data even with
smaller windows. I think the clue is the plan here.
The ST_Intersects geography function seems to be treated as a
blackbox rather than a transparent function composed of && and _ST_Distance
The magic of the geometry ST_Intersects is that the query plan can see
into the function and decomposes it into
&& + _ST_Intersects
Right. I'd quite like to see the explain analyze plan generated when
performing the ST_Intersects() substitution manually, e.g.
explain analyze select count(*) from wastac.t_tile_geometry where
border && ST_GeographyFromText('SRID=4326;POLYGON((116.751709
-31.381779,116.883545 -32.676373,114.741211 -32.796510,114.796143
-31.316101,116.751709 -31.381779))') AND _ST_Distance(border,
ST_GeographyFromText('SRID=4326;POLYGON((116.751709
-31.381779,116.883545 -32.676373,114.741211 -32.796510,114.796143
-31.316101,116.751709 -31.381779))'), 0.0, false) < 0.00001;
This should give us a better idea as to why this particular plan is
being chosen.
ATB,
Mark.
--
Mark Cave-Ayland - Senior Technical Architect
PostgreSQL - PostGIS
Sirius Corporation plc - control through freedom
http://www.siriusit.co.uk
t: +44 870 608 0063
Sirius Labs: http://www.siriusit.co.uk/labs
_______________________________________________
postgis-users mailing list
postgis-users@postgis.refractions.net
http://postgis.refractions.net/mailman/listinfo/postgis-users
